The need for water-permeable large area structures is substantial. By large area structure is meant a structure of sufficient area to substantially interfere with the natural drainage patterns in a typical one block area. Typically, any structure covering more than about 400 square yards can cause such interference.
As construction with conventional, water-impermeable concrete has increasingly covered the natural flood plain in urban and suburban areas with large area roadways, parking lots and plazas, the capacity of these flood plains to absorb water has been greatly reduced, aggravating problems of flood and pollution control.
In addition, when proper drainage is given adequate consideration, conventional water-impermeable concrete structures are complex to build and highly inefficient. Conventional concrete roadways, for example, must be constructed as composite structures including one or more layers of loose aggregate under the concrete to permit water to drain across the roadway. In addition, such roadways typically require the digging of drainage ditches and the placement of tiles at frequent points. Moreover, such structures must often be provided with a convex grade to facilitate the flow of water from the surface. Other large area structures, such as parking lots, also present similar drainage problems and often seriously alter the natural drainage patterns throughout the surrounding area.
Accordingly, there is a need for large area concrete structures adapted in configuration and composition for monolithic casting with integral drainage elements.